The invention relates to an apparatus for producing casting moulds of the type consisting of a row of identical mould parts stacked closely together and having at least one pouring cavity at each joint in the mould. The apparatus comprises a device with a pressing chamber for the successive production of the mould parts by the compression of sand or a similar material between a pressure plate and a counter-pressure plate, and at least one guideway on which the mould parts are stacked together and advanced stepwise. During this stepwise advance the casting mould passes a pouring station and subsequently a cooling path of a suitable length and, finally, the castings can at a knocking-out station be separated from the mould sand or the corresponding material.
The most commonly known apparatus of this kind comprises a stationary pressing chamber which is flush with the guideway and in which the pressure plate and the counter-pressure plate constitute movable end walls. Above the pressing chamber, a hopper is mounted, from which sand is shot into the chamber by means of compressed air. The complete cycle or process consists of a total of six successive operations, viz. the shooting of the sand into the chamber, the compression of the mould sand by the pressure plate being moved against the counter-pressure plate, the opening of the chamber by the counter-pressure plate being withdrawn and swung away after the compression pressure has been relieved, the advance of the mould part from the chamber to the guideway by means of the pressure plate, the withdrawal of the pressure plate into its initial position, and the closing of the chamber by return motion of the counter-pressure plate. The fourth and the fifth of these operations are usually the most time-consuming, because it involves relatively long travels of the pressure plate, and because the movement of the said plate, at any rate during the last part of the advance stroke and the commencement of the return stroke, must be performed slowly out of regard to the careful addition of the new mould part to the casting mould already formed and the subsequent careful withdrawal of the pressure plate from this mould part. The consumption of time will be additionally increased if the pressure plate, as it is customary, shall also contribute to the stepwise advance of the casing mould on the guideway after the addition of each mould part.
It has been attempted to increase the capacity of casting plants of the kind mentioned above, expressed in number of mould parts per unit of time, by providing two or more pressing chambers in connection with a single set of pressure and counter-pressure plates and one or two guideways.
By way of example, the specification of British Patent No. 803,332 discloses an apparatus comprising two frames incorporated in a slide which is displaceable transversely to the pressing direction, and two guideways parallel to the pressing direction. In one extreme position of the slide, a first frame is in the pressing position in relation to the pressure and counter-pressure plates, while the second frame is in the delivery position in relation to one of the guideways, and in the other extreme position of the slide the first frame is in the delivery position in relation to the other guideway, while the second frame is in the pressing position.
Another example is known from the specification of Danish Patent No. 127,044 which discloses an apparatus comprising a plurality of frames which are arranged in a circular series on a table that can be rotated by steps. During the movement of the said table each frame passes successively a pressing position between a set of pressure and counter-pressure plates, one or more core insertion positions and an ejection position in which the mould parts with the cores placed in them are ejected onto a guideway for the successive formation of the casting mould.
Common to these two prior art structures is that the pressing of the mould parts occurs alternately in two or more frames which in addition serve for conveying the mould parts to the guideway or pouring track or tracks. In this way an increase in production capacity may be achieved but there is also an increased risk of differences in shape between the successively produced mould parts, since there may be differences in tolerance between the frames, or differences may occur due to varying wear during the operation of the apparatus. Another element of risk is that the frame are not fixed with the necessary precision in the pressing position, which may also load to inaccuracies in the castings produced.